This book explores the magnetic interaction involved in the stripline circulator’s operation, the nature of the microwave resonator shape, and the network problem that arises in coupling the microwave resonator to the microwave circuit. Written by an international authority on non-reciprocal microwave circuits and devices, the book is organized into blocks of chapters that focus on specific effects and circuit aspects of the stripline circulator. Topics include: spatial shape demagnetizing factors of magnetic insulators; standing wave solutions of wye gyromagnetic planar resonators; lumped element circulators; negative permeability tracking and semi-tracking circulators; four-port single-junction circulators; and fabrication of very weakly and weakly magnetized microstrip circulators.